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AirTraffic Control Developmentat Lincoln LaboratoryJohn C. FieldingII Lincoln Laboratory-developed air traffic control technologies, which weredescribed in the Fall 1989 issue of this journal, are now in operational use.These technologies include the Mode-Select beacon system, the TrafficAlertand Collision Avoidance System, the Precision RunwayMonitor system, theTerminal DopplerWeather Radar, and the Moving Target Detector signalprocessor used in the current generation ofAirport Surveillance Radars. Ournewest efforts focus on utilization of the Global Positioning System for bothnavigation and surveillance, and on the development of automation aids for airtraffic control and management.

SNCE THE PUBLICATION of the first LincolnLaboratory Journal special issue on Air TrafficControl in 1989, several systems developed byLincoln Laboratory have come into operational use.The Traffic Alert and Collision Avoidance System(TCAS) described in William Harman's 1989 articleis now installed on all scheduled passenger airlinersthat carryover twenty-nine passengers in the UnitedStates. Several "saves" (avoided near misses or collisions) have been credited to TCAS by pilots. Theproblem of the interaction between the automaticallygenerated maneuver advisories and the normal airtraffic control process was underestimated, but thisproblem has been mitigated by providing more training for the air traffic controllers affected, and it willeventually be solved by automatic display of resolution advisories to the controllers. A version ofTCASfor smaller airliners is now being deployed. A moreadvanced TCAS, which will support horizontal aswell as vertical avoidance maneuvers and which willuse a GPS-based form ofAutomatic Dependent Surveillance rather than aircraft-based interrogation, isnow under development. This advancedTeAS is discussed in the article by Douglas Burgess in this issue.The Mode S beacon system described in Vincent

Orlando's 1989 article is now in active deployment

with eight interrogator sites fully commissioned outof a total of 148. All of the large airliners in the United States now have Mode S transponders as a consequence of the installation ofTCAS equipment. Thearticle by Steven Bussolari in this issue describes howLincoln Laboratory is working with UNISYS to ex-ploit the data-link capability of the Mode S system toprovide automated information services to the pilotsof general-aviation aircraft. Vincent Orlando's articleon the Global Positioning System (GPS) Squittershows how the Mode S transponders will be used (ex-ploiting a concept first promulgated by Paul Drouilhet, Jr.) in conjunction with GPS to provide Automatic Dependent Surveillance.

The primary radar technology described in the1989 article by Melvin Stone and John Anderson isnow widely deployed in the Airport Surveillance Ra-dar 9 (ASR-9) built byWestinghouse Electric Corporation. James Pieronek's article in this issue describesan upgrade to the ASR-9 that incorporates more re-cent technology and algorithms into the radar by using a cleverly engineered replacement of circuitboards. The new processing capability improves thetraffic-handling and fixed-clutter-rejection capabilityof the ASR-9 and provides a means of dealing moreeffectively with a changing clutter environment (e.g.,

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FIELDINGAir Traffic Control Development at Lincoln Laboratory

highway traffic, anomalous propagation, and birds).The Parallel Runway Monitor (PRM) work de

scribed by Raymond LaFrey in 1989 has resulted in areduction from 4300 feet to 3400 feet of requiredrunway separation for independent simultaneous operation of parallel runways in bad weather. The articleby Eric Shank in this issue shows how this reductionin separation can be done safely by using better monitor sensors and displays and an automated alarm sys-tem. The PRM design was recently put into service atthe new Denver International Airport to support triple-runway simultaneous IFR approaches.

The Terminal Doppler Weather Radar (TDWR)built by Raytheon and now commencing to providewind-shear protection at forty-five airports in theUnited States incorporates the Lincoln Laboratorydeveloped clutter-detection and microburst-detectionalgorithms described in the 1989 special issue of theJournal. The article on TDWR by James Evans andDavid Bernella in this issue describes subsequent fielddemonstrations to validate the Raytheon design andexamine performance in additional meteorologicalregimes; the article also describes assistance in site adaptation for the operational TDWRs.

The principal current focus for terminal aviationweather research at Lincoln Laboratory is the reduction of delays caused byweather and the prediction ofhazardous weather phenomena by integrating datafrom various terminal-area sensors (e.g., Dopplerweather radars, surface sensors, aircraft measurements, and lightning data). An overview article byJames Evans and Elizabeth Ducot describes the motivation for and design of the Integrated TerminalWeather System (ITWS) as well as the results of initial ITWS operational testing at major airports. Additional articles by Marilyn Wolfson, Edward Chornoboy, and Rodney Cole describe the ITWSalgorithms for predicting microbursts, tracking stormcells, and determining the winds aloft throughout theterminal area. Tests using the Lincoln LaboratoryITWS prototypes have conclusively demonstratedthat a significant reduction in delays caused by thunderstorms can be achieved at major airports.Prevention of collisions involving aircraft on the

airport surface is the subject of three articles in this is-sue, one by James Eggert and two by Harald Wil-

148 THE L INCOLN LABORATORY JOURNAL VOLUME 7. NUMBER 2,1994

helmsen. Some of the algorithms developed for theLincoln Laboratory demonstration of the RunwayStatus Light System at Logan International Airport inBoston have been licensed to Raytheon for incorporation into a system currently being installed in India.The aviation infrastructure in the United States isundergoing a major transition characterized by theuse of automated systems to increase capacity, reducedelay, and improve equipment maintenance. Automated advisories to pilots from the TCAS system arenow in use; auromated alarms are part of the PRMand the Surface Traffic Automation programs that arenow being installed. The restructuring of the en routeair space-the "free flight" concept-will be supported by an auromated system to detect and resolve conflicts between aircraft. An early simulation effort, described in the article by Martin Eby, shows that an enroure "free flight" environment does not require frequent course changes to ensure safe separation. Themajor difficulties to be overcome are the maintenanceof system safety and the devising ofworkable transitions to the restructured operations. A developmentprogram to provide automation aids for runway assignment and aircraft sequencing to terminal air traffic controllers is discussed in the article by HermanVandevenne. The application ofmachine-intelligencetechniques developed for the maintenance ofmilitarycommunications systems to the air traffic control radar and communications infrastructure is discussedin the article by Harold Heggestad.

The work reported in this issue was sponsored bythe Federal Aviation Administration. There are twohundred people in the three groups that comprise theLincoln Laboratory effort in Air Traffic Control. Weappreciate the opportunity to work on such interesting and important technical problems.

John C Fielding is the Associate Head of the Surveillance andControl Division at Lincoln Laboratory.